I. Field of the Invention
The invention concerns a process and a mounting frame for the insertion and exchange of filter elements for suspended matter for nuclear installations.
II. Description of the Prior Art
Today's modern nuclear installations necessitate the cleaning of increasingly larger amounts of air of radio-active contaminants and of other suspended matter, which is injurious to health. Special care has to be taken not to let any of these noxious materials escape into the atmosphere. In addition, these noxious materials should not come in contact with the maintenance personnel, in order to exclude any influence, which could be dangerous to health.
Filter elements, which are suitable for the purposes, are known. It is known to arrange such a filter element in a box-type housing, which is inserted sideways in a filter channel. The filter elements for suspended matter are inserted into the housing in a prone position through a door, which can be closed air-tight, and which is positioned in a wall of the channel. The filter elements for suspended matter are kept in place in a tight position in the housing by means of suitable tightening devices at their edge. The door opening of the housing is encircled by a ring on top of which a protective bag made of plastic is attached, in order to enable the maintenance personnel to change the radioactive contaminated filter elements without harming themselves. After the door has been opened and the tightening devices of the filter element have been loosened, the filter element is pulled into the protective bag, which is heat sealed afterwards, thus, enclosing the contaminated filter element airtight in the bag and at the same time closing the door opening with the rest of the protective bag which is also sealed off. When a new filter element is inserted, a new protective bag which contains the filter element is attached on top of the ring and slipped over the sealed-off rest of the bag of the previous filter element. This rest of the bag is then pulled into the new bag and the new filter element is inserted through the door opening into the housing. Then the tightening device is activated and the door is closed. Although these known housings offer sufficient protection for the maintenance personnel, they necessitate additional equipment, in order to separate the clean-air-side from the dusty-air-side during the changing of the filter. For this purpose flaps or gates are used, which are inserted into the housing prior to the changing of the filter in such a way that they separate the dusty-air-side from the clean-air-side. However, these separating gates are contaminated by the dusty-air-side during the changing of the filter element, because they have to contact the dust particles, which are harmful to health. These dust particles can contaminate the clean-air-side when the gates are removed from their closed position. These known housings are extremely expensive and, due to the maintenance operation, which is described above, do not offer an absolutely safe protection against contamination of the clean-air-side with radioactive material. These known housings have already been combined to form an insertable wall, which can be inserted in an opening in the wall, by arranging these housings adjacent to each other in rows, with the filters of the filter elements in their housings being arranged parallel to the stream of air. In order to pass the air through the filter layer from the dusty-air-side to the clean-air-side, between each two housings, which are located one above the other, deflecting plates for the air are installed, which lead from the upper edge of the lower housing on an incline to the opposite lower edge of the upper housing. These deflecting plates, which are arranged on both sides of the housing, form an entrance orifice for the dusty-air-side. In this way the air is forced by the deflecting plates to pass the filter layer. These known walls, which consist of housings, have the same disadvantages, since the changing of the contaminated filter elements is performed in the same way as described above. If a direct contact between the dusty-air-side and the clean-air-side must be prevented during the changing of the filter elements, it is necessary to install flaps or gates on the dusty-air-side or on the clean-air-side in front of the air entrance orifices or air exit orifices of the housings. These gates or flaps cause a relatively high additional effort and nevertheless cannot reliably prevent a contamination of the clean-air-side, for reasons which were described above, since the radioactive materials, which were possibly deposited on the gates or flaps could be transferred to the clean-air-side, when these gates or flaps are opened.
In order to avoid the large effort, which is necessary for the known housings, the filter elements for suspended matter were arranged in so-called frames, which are attached to a channel or to an opening in the brick wall. These frames consist of individual frames, which have a capacity for one filter element for suspended matter, and which are arranged adjacently above and beside each other to form a filter installation. The filter elements for suspended matter are inserted into the individual frames in an upright position. The frames consist of angle irons, which are equipped with flip-down tightening devices for the filter element for suspended matter and with a fluted frame, which permits testing for leaks, to which the filter element is clamped by means of the tightening devices in a tight position. The tightening devices are constructed in such a way that they retighten automatically, in order to guarantee a permanently leak-proof fitting of the filter element to the fluted test frame. The necessary changing of the filter elements for suspended matter necessitates a substantial effort with these frames. Since the contaminated filter elements must not be contacted with the clean-air-side for reasons which are self explanatory, the changing must be done from the dusty-air-side. This necessitates special safety measures and protective measures for the personnel who are performing these changings. The contaminated filter elements must be removed from the frame and removed from the space on the dusty-air-side by personnel equipped with appropriate protective clothing. The filter elements are removed through openings in a side wall of the room, which are equipped with air-locks. One of these openings is necessary for the removal of the contaminated filter elements, and another one is necessary for the supplying with a new filter element. The contaminated filter elements are put through the opening in the wall into a protective bag, which is mounted on a ring. The bag is heat sealed after insertion of the filter element. The performance of the changing of the filter elements from the dusty-air-side presents a substantial disadvantage and risk, due to the necessary effort, due to the eventual endangering of the maintenance personnel, and due to the transfer of the remainder of the bag in very close vicinity to the actual filter element. However, another disadvantage, which is even more substantial, consists of the fact that the dusty-air-side is in direct contact with the clean-air-side during the changing procedure by means of the orifices of the individual frames. In this way dust particles, which are harmful to health or radioactive, can get to the clean-air-side. So far one had to live with this disadvantage. This disadvantage was minimized as much as possible by performing the exchange of the contaminated filter elements for new filter elements in rapid succession. A number of persons are therefore necessary for the performance of such an exchange. In certain instances the orifices on the clean-air-side were closed by lids before the maintenance work was performed. However, the same problems with regard to contamination are encountered, as described above.
The invention is based on the objective to avoid these disadvantages, which are encountered for the known frames and housings with deflector plates, and to enable a changing of the filter elements during which the dusty-air-side and the clean-air-side are separated in the simplest way. Furthermore, the invention is based on the objective to perform the insertion and exchange of the filter elements for suspended matter from the clean-air-side, without contamination of the new protective bag and the newly exchanged filter element. This problem is solved by the process of the present invention.